Interfacing metals and compounds for enhanced hydrogen evolution from water splitting
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Introduction With the rapid growth of global energy demands and increasing environmental concerns, intense research efforts have been devoted to exploring sustainable and “green” energy sources as viable alternatives to fossil fuels.1–6 Among these approaches, renewable energy-driven H2 evolution from electrocatalytic water splitting is considered a promising pathway because of the zero carbon release nature of this process as well as the high gravimetric energy density of H2.7–15 The H2 evolution reaction (HER) is the reductive half-reaction of water electrolysis, which is generally carried out under either strong acidic or alkaline conditions for better electrolyte conductivity.16,17 HER at low pH (2H+ + 2e– ↔ H2) typically exhibits high energy efficiency and requires a compact design with proton exchange membranes. Nevertheless, the limited scope of suitable low-cost electrocatalysts under strongly acidic conditions and potential degradation of the membrane restrict its wide application. On the other hand, H2 production in alkaline electrolytes (2H2O + 2e– ↔ H2 + 2OH–) shows unique advantages, such as a wider library of suitable earth-abundant electrocatalysts. Nevertheless, the overall performance of HER under alkaline condition is largely limited by the sluggish kinetics of
water adsorption and dissociation, leading to low efficiency, high overpotential, and large energy consumption.16 To date, significant efforts have been made to develop competent lowcost electrocatalysts for HER with high activity and long durability. A large number of catalyst candidates, including metals, alloys, and metal compounds, have been explored for effective H2 production from water electrolysis. Among many design approaches in achieving competent HER electrocatalysts, interface engineering has emerged as an effective strategy, which can optimize the adsorption/desorption of catalytic intermediates, accelerate electron transfer, and stabilize active sites.16,18–20 Various combinations of metals (Pt, Au, Ru, Rh, Pd, Ni, Co, Fe, Cu), alloys (Ni-Co, Ni-Mn, Ni-Mo), and compounds (oxides, hydroxides, phosphides, selenides, nitrides, sulfides, borides, and carbides) have been developed as electrocatalysts for HER.21–23 In general, there are three types of hybrid electrocatalysts with different interfaces: metal/metal, metal/compound, and compound/compound. Herein, we focus on interfacial electrocatalysts consisting of metal/compound interfaces. We particularly highlight their synthesis methods, reaction mechanisms, and electrocatalytic activities for HER. This article is structured primarily into two
Jian-Hong Tang, University of Cincinnati, USA; [email protected] Yujie Sun, University of Cincinnati, USA; [email protected] doi:10.1557/mrs.2020.169
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